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Seyfi, Sahand | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43716 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Lateral spreading is a common mode of earthquake-induced failure that usually occurs as a result of liquefaction in gently sloped sandy layers. Numerical simulation of this phenomenon requires fully coupled analysis of displacement of solid sand particles and pore water pressure under seismic loading. Predicting occurrence of initial liquefaction and sub-sequent ground movement requires employing an efficient and robust constitutive model that can predict the undrained behavior of saturated sand under different conditions. In this study, a fully coupled finite element code “PISA” utilizing a critical state two-surface plasticity constitutive model, proposed by Manzari and Dafalias (1997), has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the monotonic and cyclic triaxial experiments under drained and undrained conditions and two creditable centrifuge experiments.
    After getting confidence of the accuracy of the results of horizontal and vertical displacement and excess pore pressure, this model has been used for a comprehensive parametric study. Effects of different geometries and loadings on lateral spreading have been investigated in this numerical study. Numerical modeling of four different geometrical forms of surface and subsurface of liquefiable layer indicates that the effect of surface inclination angle on the lateral displacement is approximately greater than 2.0 times the base slopes and the amount and direction of lateral spreading are noticeably affected by the geometrical conditions. The obtained results indicate that for irregular geometry of the sand layer, the direction of lateral spreading in lower and upper soil parts of layer follow the direction of the base inclination and surface slope, respectively. Parametric studies by the developed numerical model show that the effects of layer height, relative density and loading frequency on the level of lateral spreading are approximately same for the examined geometrical condition. For all geometry conditions, the surface displacements increase with increase of acceleration. Numerical results indicate that increasing the acceleration from 0.1g to 0.2g results in significant increase of lateral displacement; however, for higher accelerations, the difference between the obtained final surface displacements is not considerable. Parametric study on height of liquefiable layer shows that for all geometry conditions the rational result is increasing of lateral displacement by increasing the height of the layer. The numerical results also indicate that the frequency of the excitation has significant effects on lateral spreading of the sand layer, especially for lower frequencies.
    To examine the capability of the developed code “PISA” in simulating the seismic behavior of gravity quay walls, numerical modeling of a centrifuge experiment was considered. The results show that the values of predicted wall tilting, horizontal displacement and maximum excess pore water pressure is in good agreement with experimental records
  9. Keywords:
  10. Liquefaction ; Numerical Modeling ; Parametric Study ; Lateral Spread ; Fully Coupled Two-Dimensional Dynamics Analysis ; Cravity Guag Wall

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